1. Field of the Invention
The present invention relates to a braking device of a uniaxial positioning table apparatus mounted on a machine tool, an industrial robot or the like so as to position and guide a object (a driven object) with a high-accuracy, and especially, of a linear motor positioning table apparatus having a linear electromagnetic actuator as a driving source (hereafter, referred to simply as a linear motor table).
2. Description of the Prior Art
In FIG. 1, a linear motor table of the prior art is shown.
As shown in FIG. 1, the linear motor table has a long rectangular bed 1 and a table 2 moving on the bed 1 in the longitudinal direction, and a plurality of rollers installed in the table 2 rolls along a track (not shown in the figure) formed in the longitudinal direction of the bed 1, so that the table 2 may be guided along the bed 1.
Furthermore, the detecting means for detecting the position of the table 2 relative to the bed 1 comprises a linear scale 4 provided on the overhang portion 1a, which is formed at one side portion of the bed 1, a light emitting element 5a and a light receiving element 5b attached through a bracket 2a to the side portion of the table 2 corresponding to the overhang portion 1a.
The linear motor table is composed of a linear direct current motor, which comprises a primary side composed of a plurality of armature coils 7 arranged on the bed 1 along the longitudinal direction and a secondary side composed of a field magnet (not shown in the figure) attached to the under surface of the table 2 facing the armature coils 7.
The field magnet is magnetized so that a plurality of magnetic poles N and S may be arranged by turns in the direction of movement of the table 2.
The linear motor table feeds each armature coil 7 at a prescribed timing, so that the table 2 may move in the longitudinal direction of the bed 1, and the positioning action may be performed at a desired position on the basis of the detection signal of the detecting means.
The linear motor table has a problem in that it performs stopping and positioning of the moving table 2 only by the magnetic force, so that no braking force may operate when the electrical feed is cut off because of a power failure or the like and the table 2 cannot perform stopping and positioning and may move.
Especially, there is such a problem that the table 2 may drop on an occasion when the linear motor table is used in a state of a vertical axis (the direction of operation is vertical) or in a state of an approximately vertical axis so that the electrical feed may be cut off.